Two sets of arrows on the Noctua nh-d15?

[ai8den]

The fans themselves have two sets of arrows and I'm not sure which to follow. The arrows all along the inside of the fan housing or the arrows on the bottom that has one arrow in a horizontal and one in a vertical direction?

Edit: I found a thread with the answer

 

[synphul]

You mean for direction of airflow? If so almost every fan (unless there's an odd one out there) works the same way. One side of the fan has just the blades, the other side has the supports/struts that the fan hub is mounted to. The exposed side of the fan is the intake and the side with the supports is exhaust.

 

[ai8den]

Thanks, all along the inside of the rim there appear to be little arrows as well and that's what made me uncertain which to follow but this deffinately helps 😀

 

[synphul]

Yea they're supposed to make it easier to identify which way to face the fan. It's not a terrible idea but most every fan I've run across follows the same design and rotation of the pics I posted. Makes it really easy to identify airflow direction of pretty much any fan whether it has the arrows or not, the air flows toward the support framework so if you have a nice clear view of the whole fan blade you're looking at the intake side.

I'm not sure if looks is the reason for it or not but in windowed cases it pretty much ensures that you have a nice view of the fan from most angles in the vast majority of setups. Whether it's the cpu fan on an air cooler, the rear exhaust fan, case intake fans viewed through a ventilated front case panel or whatever. You're always seeing the more 'decorative' side of the fan rather than the supports and wiring.

Maybe it's just a happy accident, it could be due to airflow that a fan has an easier time collecting air from the unobstructed side and pushing it past the supports.